In recent years, various display apparatuses and technology for displaying images of different sizes and shapes have been developed. For example, there is known AR (Augmented Reality) technology in which an image captured by a camera mounted on an HMD (Head Mount Display), a smartphone, or a tablet-type terminal is used (see, for example, Japanese Laid-Open Patent Publication No. 2012-103789). For example, AR technology may be used to overlay object data identified by a mark captured by a camera with scenery or the like of a reality space and display the overlaid data.
The HMD has a structure in which a screen is positioned in front of the eyes of the user. This structure of the HMD causes difficulty in enabling the user to perform input control by directly touching the screen. In contrast, a terminal such as a smartphone allows the user to easily perform input control by directly touching the screen of the terminal. However, in a case of working with both hands while viewing the screen of the terminal, an input operation besides the touch operation is preferable from the standpoint of improving work efficiency. The use of gestures or a controller are considered as examples of input operations besides the touch operation. However, because these examples still require the use of the user's hands for performing gestures or operating the controller, it is difficult for the user to perform an input operation while working with both hands. In contrast, an input operation using audio recognition enables the user to perform an input operation while working with both hands.